Design Methodologies for Low Flux Density, High Efficiency, kW Level Wireless Power Transfer Systems with Large Air Gaps

The objective of this work is to investigate resonant circuit and magnetic component design methodologies for multi-kW, MHz frequency, over 95% coil-to-coil efficiency, and large distance (20~40cm) wireless power transfer systems that achieve very low flux density in the air-gap. Design methodologies for resonant circuits as a part of a magnetically coupled system using lumped parameter equivalent circuit models have been proposed. A new design concept, the feasible design space, has been proposed which shows the combinations of the transmitter and receiver coils reactances that satisfy given voltage and current limits of the circuit. Using the feasible design space, the transmitter and receiver coil geometries which result in low flux density, high efficiency, high control stability, etc. have been calculated. The trade-offs between the system performances vs. transmitter and receiver coil geometries design have been demonstrated graphically. The optimal transmitter and receiver coils geometries have been selected from a new objective function. The proposed design methodology has been evaluated by means of FEA and experimental analysis. As a second focus of this research, a new magnetic component design methodology for improving power transfer efficiency at MHz operation has been investigated in this research. A new conductor layout methodology called surface spiral winding (SSW) was proposed and FEA models showed that it is effective in decreasing Ohmic losses and in increasing coupling coefficient between the transmitter and receiver. Design methodologies for the SSW coils have been proposed using analytical equations and FEA results. The proposed design methodologies have been evaluated via FEA and experimental analysis. Thermal modeling of the SSW coils has been developed and experimentally evaluated.;In the last part of this research, the impact of coil misalignment is investigated. By assuming the transmitter and the receiver coils as filaments, the mutual inductance of large air-gap wireless power transfer systems has been calculated. The analytical mutual inductance calculation was evaluated by FEA and experiments. The impacts of coil misalignment on the magnetic flux density, resonant frequency, power capability and efficiency have been investigated and the theoretical analyses were evaluated by means of FEA and experimental results.